Thrust shaft for ram air fan

ABSTRACT

A thrust shaft contains a shaft body having a disk at one axial end to provide a rotating surface in a thrust bearing, the disk having a first side and an opposite second side. The thrust shaft also contains a first section extending from the first side of the disk, the first section cylindrical in shape and having eleven holes uniformly spaced circumferentially about the first section, the holes being substantially axially equidistant from the first side of the disk. The thrust shaft also contains a second section cylindrical in shape having a smaller diameter than the first section, the second section extending from the first section to an end of the shaft remote from the disk.

BACKGROUND

The present invention relates generally to an environmental control system. More particularly, the invention relates to a thrust shaft of a ram air fan assembly for an environmental control system for an aircraft.

An environmental control system (“ECS”) aboard an aircraft provides conditioned air to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high so that the air is desired to be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired but at such a low pressure that the air must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that the air must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the ECS before the air is delivered to the aircraft cabin. As heat is removed from the air, the heat is dissipated by the ECS into a separate stream of air that flows into the ECS, across one or more heat exchangers in the ECS, and out of the aircraft, carrying the excess heat with it. Under conditions where the aircraft is moving fast enough, the pressure of air ramming into the aircraft is sufficient to move enough air through the ECS and over the heat exchangers to remove the excess heat.

While ram air works well under normal flight conditions, at lower flight speeds, or when the aircraft is on the ground, ram air pressure is too low to provide enough airflow across the heat exchangers for sufficient heat removal from the ECS. Under these conditions, a ram air fan within the ECS is employed to provide the necessary airflow across the ECS heat exchangers.

As with any system aboard an aircraft, there is great value in an improved ram air fan that includes innovative components designed to improve the operational efficiency of the ram air fan or to reduce weight.

SUMMARY

A thrust shaft contains a shaft body having a disk at one axial end to provide a rotating surface in a thrust bearing, the disk having a first side and an opposite second side. The thrust shaft also contains a first section extending from the first side of the disk, the first section cylindrical in shape and having eleven holes uniformly spaced circumferentially about the first section, the holes being substantially axially equidistant from the first side of the disk. The thrust shaft also contains a second section cylindrical in shape having a smaller diameter than the first section, the second section extending from the first section to an end of the shaft remote from the disk.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a cross-sectional view of a ram air fan assembly.

FIG. 1 b is an enlarged cross-sectional view of a portion of the ram air fan assembly in FIG. 1 a, schematically illustrating cooling airflow paths.

FIG. 2 is a perspective view of a thrust shaft of the ram air fan assembly.

FIG. 3 is a cross-sectional view through the thrust shaft, taken along line 3-3 of FIG. 2.

While the above-identified figures set forth embodiments of the present disclosure, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features and components not specifically shown in the drawings.

DETAILED DESCRIPTION

FIG. 1 a illustrates ram air fan assembly 10 incorporating the present invention, while FIG. 1 b shows a view of ram air fan assembly 10 concentrated on the cooling airflow paths. Ram air fan assembly 10 includes fan housing assembly 12, inlet housing 16, outer housing 18, and inner housing 20. Fan housing 12 includes fan struts 22, motor 24 (including motor rotor 25 and motor stator 26), back iron 27, thrust shaft 28, thrust plate 30, thrust bearings 32, tie rod 38, and journal bearings 40. Other components include bearing housing 14, journal bearing shaft 34, and shaft cap 36. Inlet housing 16 contains bladed fan rotor 42 and shroud 44, in addition to a portion of tie rod 38. Outer housing 18 includes terminal box 46 and plenum 48. Within outer housing 18 are diffuser 50, motor bearing cooling tube 52, and wire transfer tube 54. A fan inlet can be a source of air to be moved by ram air fan assembly 10 in the absence of sufficient ram air pressure. A bypass inlet can be a source of air that moves through ram air fan assembly 10 when sufficient ram air pressure is available. A cooling inlet can provide cooling air to ram air fan assembly 10 when necessary.

As illustrated in FIG. 1 a, inlet housing 16 and outer housing 18 are attached to fan housing 12 at fan struts 22. Bearing housing 14 is attached to fan housing 12 and inner housing 20 connects motor bearing cooling tube 52 and wire transfer tube 54 to bearing housing 14. Motor bearing cooling tube 52, through which cooling air enters ram air fan 10, connects inner housing 20 to a source of cooling air at outer housing 18. Wire transfer tube 54 connects inner housing 20 to outer housing 18 at terminal box 46. Motor stator 26 and thrust plate 30 attach to fan housing 12. Motor rotor 25 and motor stator 26 are contained within motor 24. Motor 24 is radially positioned about journal bearing shaft 34, which connects shaft cap 36 to thrust shaft 28. Journal bearing shaft 34 defines an axis of rotation about centerline C for ram air fan assembly 10 and thrust shaft 28 can be positioned coaxially about centerline C. Bladed fan rotor 42 is attached to thrust shaft 28 with tie rod 38 extending along the axis of rotation (centerline C) from shaft cap 36 at the end of journal bearing shaft 34 through journal bearing shaft 34 and thrust shaft 28 to bladed fan rotor 42 and shroud 44. Suitable fasteners, such as threaded nuts (not shown) can secure shaft cap 36 to journal bearing shaft 34 on one end of tie rod 38 and shroud 44 to bladed fan rotor 42 at the opposite end of tie rod 38. Thrust plate 30 and fan housing 12 contain disk 56 (shown in FIG. 2) of thrust shaft 28, with thrust bearings 32 positioned between disk 56 of thrust shaft 28 and thrust plate 30 and between disk 56 of thrust shaft 28 and fan housing 12. Journal bearings 40 are positioned between journal bearing shaft 34 and bearing housing 14 and between thrust shaft 28 and fan housing 12. While the present embodiment uses these types of bearings, other types of bearings can be utilized in further embodiments. Bladed fan rotor 42, shroud 44, and a portion of fan housing 12 are contained within inlet housing 16. Diffuser 50 can be attached to an inner surface of outer housing 18. Plenum 48 can be configured as a portion of outer housing 18 that fluidically connects ram air fan assembly 10 to the bypass inlet. Inlet housing 16 is fluidically connected to the fan inlet and outer housing 18 is fluidically connected to the fan outlet.

In operation, ram air fan assembly 10 can be installed into an environmental control system (“ECS”) aboard an aircraft (or other vehicle) and connected to the fan inlet, the bypass inlet, the cooling inlet, and the fan outlet. When the aircraft does not move fast enough to generate sufficient ram air pressure to meet the cooling needs of the ECS, power is supplied to motor stator 26 by wires running from terminal box 46, through wire transfer tube 54, inner housing 20, and bearing housing 14. Energizing motor stator 26 causes motor rotor 25 to rotate about the axis of rotation (centerline C) of ram air fan assembly 10, rotating connected journal bearing shaft 34 and thrust shaft 28. Bladed fan rotor 42 and shroud 44 also rotate by way of their connection to thrust shaft 28. Journal bearings 40 and thrust bearings 32 help provide low friction support for the rotating components (as will be discussed with regards to FIG. 2). Rotation of bladed fan rotor 42 can move air from the fan inlet, through inlet housing 20, past fan struts 22 and into the space between fan housing 12 and outer housing 18, increasing the air pressure in outer housing 18. As the air moves through outer housing 18, air flows past diffuser 50 and inner housing 20, where the air pressure is reduced due to the shape of diffuser 50 and the shape of inner housing 20. Once past inner housing 20, the air can move out of outer housing 18 at the fan outlet.

Components within bearing housing 14 and fan housing 12, especially thrust bearings 32, journal bearings 40 and motor 24, can generate significant heat and generally must be cooled. Cooling air can be provided by motor bearing cooling tube 52 which directs a flow of cooling air to inner housing 20. Inner housing 20 directs flow of cooling air to the assembly, where cooling air flows past components in fan housing 12, cooling thrust bearings 32, journal bearings 40, and other ram air fan components. As FIG. 1 b shows, flow of cooling air follows three paths as cooling air moves from cooling tube 52 to bladed fan rotor 42, where the cooling air exits fan housing 12. Cooling air is able to flow (a) through a space between motor stator 26 and back iron 27 (designated flow F1); (b) through a space between motor stator 26 and motor rotor 25 (designated flow F2); and (c) through a core within journal bearing shaft 34 and thrust shaft 28 centered about tie rod 38 (designated flow F3). The cooling air helps reduce a risk of overheating, which in turn helps reduce or prevent wear, deformation, and failure from excess heat. The present inventors have discovered that increasing the penetration of and control over the cooling airflow is important, particularly in the core (including thrust bearings 32 and inner diameter of bladed fan rotor 42). Thrust shaft 28, as is shown in FIG. 2, provides increased control of the cooling airflow and more penetration of cooling air to areas of need through the utilization of airflow holes.

FIG. 2 is a perspective view of thrust shaft 28 of ram air fan assembly 10, while FIG. 3 is a cross-sectional view through thrust shaft 28 taken along line 3-3 of FIG. 2. Thrust shaft 28 includes disk 56; first section 58, which can be cylindrical in shape; second section 60, which can be cylindrical in shape; and third section 64, which can be cylindrical in shape and is shown in FIG. 3. Airflow holes 62 are provided in first section 58.

Disk 56 is centered about centerline C, as are the other components of thrust shaft 28. At the center of disk 56 is a circular hole centered about centerline C and tie rod 38. Attached to disk 56 circumferentially about the circular hole at the center of disk 56 is first section 58. First section 58 can be cylindrical and includes airflow holes 62, which can be uniformly spaced circumferentially about first section 58 and can extend completely through first section 58 in a generally radial direction. First section 58 extends axially from disk 56 and adjoins second section 60. Second section 60 can be cylindrical and is centered radially about centerline C and tie rod 38.

Thrust shaft 28 also includes third section 64, which can be cylindrical and adjoins disk 56 opposite first section 58. Third section 64 extends radially away from disk 56 and is centered about centerline C and tie rod 38. Third section 64 can be large enough so as to attach to disk 56 without interfering with the circular hole at the center of disk 56. While any suitable material and method of manufacturing thrust shaft 28 can be used, the present embodiment can be machined from one unitary and monolithic metal part, such as an aluminum blank.

Thrust shaft 28 connects bladed fan rotor 42 and shroud 44 to motor rotor 25. When needed, motor 24 causes thrust shaft 28 to rotate, which in turn causes bladed fan rotor 42 and shroud 44 to rotate and increase the inflow of air into ram air fan 10. Powering the bladed fan rotor 42 with motor 24 may be desired to generate air pressure when the aircraft does not move fast enough to generate sufficient ram air pressure to meet the cooling needs of the ECS. Journal bearings 40, which are located axially outward of first section 58, keep thrust shaft 28 centered about centerline C and provide low friction support. Thrust bearings 32 are located on both sides of disk 56 and provide radial low friction support for thrust shaft 28. When thrust shaft 28 is rotating, the area of first section 58 that contacts journal bearings 40, as well as the area of disk 56 that contacts thrust bearings 32, can become hot due to friction. As mentioned earlier, this heat may cause undesired wear, deformation, and failure of thrust shaft 28.

To improve cooling airflow to thrust bearings 32 and journal bearings 40 and control over the flow of cooling air, first section 58 includes airflow holes 62. Airflow holes 62 are configured so as to control and meter cooling airflow from the core of ram air fan 10 to journal bearings 40 and thrust bearings 32 without diverting excessive cooling flow away from other components of ram air fan 10 and thereby depriving those other components of suitable cooling flows. Airflow holes 62 also allow, if needed, cooling air to flow from other flow paths into the core. The illustrated embodiment includes eleven holes uniformly spaced circumferentially about first section 58, but other embodiments can be configured so as to maximize efficient movement of cooling air throughout ram air fan 10 while also keeping thrust shaft 28 balanced to prevent vibration of thrust shaft 28 at high speed rotation. Other embodiments can vary the number, spacing, diameter, and/or other parameters of airflow hoes 62 to suit ram air fan 10 needs. Airflow holes 62 can be located anywhere radially along first section 58, but the present embodiment shows airflow holes 62 near disk 56 so that airflow holes 62 are not within the area of first section 58 around which journal bearing 40 is located.

FIG. 3 shows various dimensions of thrust shaft 28, including diameter D1 of airflow holes 62, length D2 from the center of airflow holes 62 to an adjacent face of disk 56, inside diameter D3 of third section 64, inside diameter D4 of second section 60, length D5 of first section 58, and outer diameter D6 of first section 58. By way of example, and not limitation, possible maximum and minimum ratios of these dimensions can be seen in Table 1. All values in Table 1 are approximate. Persons of ordinary skill in the art will appreciate that scaling is possible within the listed ranges to provide suitable dimensions for particular applications.

TABLE 1 Ratio Minimum Maximum D1/D2 1.0426 1.1333 D1/D3 0.1678 0.1747 D1/D4 0.1882 0.1960 D1/D5 0.0912 0.0953 D1/D6 0.1250 0.1301 D2/D3 0.1541 0.1610 D2/D4 0.1728 0.1806 D2/D5 0.0838 0.0879 D2/D6 0.1148 0.1199 D3/D4 1.1210 1.1226 D3/D5 0.5436 0.5460 D3/D6 0.7445 0.7452 D4/D5 0.4845 0.4867 D4/D6 0.6636 0.6643 D5/D6 1.3645 1.3699

The ratios in Table 1 represent one possible configuration of thrust shaft 28 that connects motor rotor 25 to bladed fan rotor 42 and shroud 44 and provides efficient cooling flow to components of ram air fan 10. In the illustrated embodiment, as can be seen most clearly in FIG. 3, diameter D4 of second section 60 is smaller than diameter D6 of first section 58, but thrust shaft 28 is not limited to such a configuration. The ratio of diameter D1 of airflow holes 62 to length D2 from the face of disk 56 to the center of airflow holes 62 allows the control of cooling air through airflow holes 62 while ensuring airflow holes 62 (particularly edges of holes 62) do not come into contact with relatively delicate journal bearings 40. Such contact could cause damage to journal bearings 40, airflow holes 62, or first cylindrical section 58. As mentioned before, including airflow holes 62 in first section 58 in the present embodiment increases efficiency of the cooling airflow system by allowing control of the flow of cooling airflow between flows F1, F2, and F3. Also, the configuration of airflow holes 62 allows increased access of the cooling air in flow F3 to components such as journal bearings 40 and thrust bearings 32.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments of the present invention.

A thrust shaft can include a shaft body having a disk at one axial end to provide a rotating surface in a thrust bearing, the disk having a first side and an opposite second side; a first section cylindrical in shape and extending from the first side of the disk, the first section having eleven holes uniformly spaced circumferentially about the first section, the holes being substantially axially equidistant from the first side of the disk; and a second section cylindrical in shape and having a smaller diameter than the first section, the second section extending from the first section to an end of the shaft remote from the disk.

The thrust shaft of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components:

a third section can be attached to the second side of the disk;

a ratio of a diameter of each of the holes to the distance measured from the first side of the disk to the center of the holes can be between approximately 1.04 and approximately 1.14;

a ratio of an axial length of the first section to an outer diameter of the first section can be between approximately 1.36 and approximately 1.37; and/or

the holes can allow airflow to cool a thrust bearing adjacent to the disk.

A thrust shaft can include a body having a disk, the disk having a first side and an opposite second side, the disk having a circular hole located at the center of the disk; a first section of the thrust shaft, the first section cylindrical in shape and having a first end and a second end, the first end attached to the first side of the disk; a second section of the thrust shaft, the second section cylindrical in shape and having a first end and a second end, the first end of the second section attached to the second end of the first section; and a plurality of holes, the holes uniformly spaced apart and located circumferentially about the first section, wherein a ratio of a diameter of each of the holes to the distance measured from the first side of the disk to the center of the holes can be between approximately 1.04 and approximately 1.14.

The thrust shaft of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:

the second section can have a smaller outer diameter than an outer diameter of the first section;

the holes can be located substantially axially equidistant from the first side of the disk;

the thrust shaft can be supplied with air by the holes;

the first section can have eleven holes uniformly spaced circumferentially about the first section;

a ratio of an axial length of the first section to the outer diameter of the first section can be between approximately 1.36 and approximately 1.37;

the holes can allow airflow to cool a bearing adjacent to the disk;

a third section that can be cylindrical in shape and can be attached to the second side of the disk; and/or

a ratio of an inner diameter of the third section to an inner diameter of the second section can be between approximately 1.12 and approximately 1.13.

A ram air fan assembly can include a fan housing; a fan motor attached to the fan housing; a fan rotor; a main shaft connecting the fan motor to the fan rotor; a thrust shaft centered about the main shaft, the thrust shaft having a disk at one axial end, the disk having a first side and a second side, a first section cylindrical in shape and having a first end and a second end, the first end of the first section attached to the first side of the disk, a second section extending from the second end of the first section to an end of the thrust shaft remote from the disk, the second section having a smaller outer diameter than an outer diameter of the first section, wherein the ratio of the length of the first section to the outer diameter of the first section is between approximately 1.36 and approximately 1.37, wherein the first section includes a plurality of holes uniformly spaced circumferentially about the first section and substantially axially equidistant from the disk.

The ram air fan assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:

the holes can allow airflow to cool a bearing adjacent to the disk;

the first section can have eleven holes;

a ratio of a diameter of the holes to distance from the disk to the center of the holes can be between approximately 1.04 and approximately 1.14;

a third section can be cylindrical in shape and can extend from the second side of the disk; and/or

the thrust shaft can have a ratio of an inner diameter of the third section to an inner diameter of the second section is between approximately 1.12 and approximately 1.13.

Any relative terms or terms of degree used herein, such as “substantially,” “essentially,” “generally,” “approximately,” and the like, should be interpreted in accordance with and subject to any applicable definitions or limits expressly stated herein. In all instances, any relative terms or terms of degree used herein should be interpreted to broadly encompass any relevant disclosed embodiments as well as such ranges or variations as would be understood by a person of ordinary skill in the art in view of the entirety of the present disclosure, such as to encompass ordinary manufacturing tolerance variations, incidental alignment variations, alignment or shape variations induced by thermal, rotational or vibrational operational conditions, and the like.

While the invention has been described with reference to an exemplary embodiment(s), the invention will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A thrust shaft comprising: a shaft body having a disk at one axial end to provide a rotating surface in a thrust bearing, the disk having a first side and an opposite second side; a first section extending from the first side of the disk, the first section cylindrical in shape and having eleven holes uniformly spaced circumferentially about the first section, the holes being substantially axially equidistant from the first side of the disk; and a second section cylindrical in shape having a smaller diameter than the first section, the second section extending from the first section to an end of the shaft remote from the disk.
 2. The thrust shaft of claim 1, wherein a third section cylindrical in shape is attached to the second side of the disk.
 3. The thrust shaft of claim 1, wherein a ratio of a diameter of each of the holes to the distance measured from the first side of the disk to the center of the holes is between approximately 1.04 and approximately 1.14.
 4. The thrust shaft of claim 1, wherein a ratio of an axial length of the first section to an outer diameter of the first section is between approximately 1.36 and approximately 1.37.
 5. The thrust shaft of claim 1, wherein the holes allow airflow to cool a thrust bearing adjacent to the disk.
 6. A thrust shaft comprising: a body having a disk, the disk having a first side and an opposite second side, the disk having a circular hole located at the center of the disk; a first section of the thrust shaft, the first section cylindrical in shape and having a first end and a second end, the first end attached to the first side of the disk; a second section of the thrust shaft, the second section cylindrical in shape and having a first end and a second end, the first end of the second section attached to the second end of the first section; and a plurality of holes, the holes uniformly spaced apart and located circumferentially about the first section, wherein a ratio of a diameter of each of the holes to the distance measured from the first side of the disk to the center of the holes is between approximately 1.04 and approximately 1.14.
 7. The thrust shaft of claim 6, wherein the second section has a smaller outer diameter than an outer diameter of the first section.
 8. The thrust shaft of claim 6, wherein the holes are located substantially axially equidistant from the first side of the disk.
 9. The thrust shaft of claim 6, wherein the thrust shaft is supplied with air by the holes.
 10. The thrust shaft of claim 6, wherein the first section has eleven holes uniformly spaced circumferentially about the first section.
 11. The thrust shaft of claim 6, wherein a ratio of an axial length of the first section to the outer diameter of the first section is between approximately 1.36 and approximately 1.37.
 12. The thrust shaft of claim 6, wherein the holes allow airflow to cool a bearing adjacent to the disk.
 13. The thrust shaft of claim 6 and further comprising: a third section that is cylindrical in shape and is attached to the second side of the disk.
 14. The thrust shaft of claim 13, wherein a ratio of an inner diameter of the third section to an inner diameter of the second section is between approximately 1.12 and approximately 1.13.
 15. A ram air fan assembly comprising: a fan housing; a fan motor attached to the fan housing; a fan rotor; a main shaft connecting the fan motor to the fan rotor; a thrust shaft centered about the main shaft, the thrust shaft having a disk at one axial end, the disk having a first side and a second side, a first section cylindrical in shape and having a first end and a second end, the first end of the first section enjoining the first side of the disk, a second section cylindrical in shape and extending from the second end of the first cylindrical section to an end of the thrust shaft remote from the disk, the second section having a smaller outer diameter than an outer diameter of the first section, wherein a ratio of the length of the first section to the outer diameter of the first section is between approximately 1.36 and approximately 1.37, wherein the first section includes a plurality of holes uniformly spaced circumferentially about the first section and substantially axially equidistant from the disk.
 16. The ram air fan of claim 15, wherein the holes allow airflow to cool a bearing adjacent to the disk.
 17. The ram air fan of claim 15, wherein the first section has eleven holes.
 18. The ram air fan of claim 15, wherein a ratio of a diameter of the holes to a distance from the disk to the center of the holes is between approximately 1.04 and approximately 1.14.
 19. The ram air fan of claim 15, the thrust shaft further comprising: a third section cylindrical in shape and extending from the second side of the disk.
 20. The ram air fan of claim 19, wherein the thrust shaft has a ratio of an inner diameter of the third section to an inner diameter of the second section is between approximately 1.12 and approximately 1.13. 